The present invention relates to an imaging method utilizing an NMR (nuclear magnetic resonance) phenomenon, and more particularly to an NMR measuring method suitable for performing a high speed spectroscopic imaging by use of a rotating field gradient.
An NMR spectroscopic imaging, which is also called a spatially resolved NMR spectroscopy, includes determining the magnetization distribution of a certain region of an object of interest as well as the spectrum of nuclear spins at each location in the magnetization distribution image. This spin spectrum represents a chemical shift with a magnetic resonant frequency which is mainly caused by the chemical coupling state of a nuclide of interest in the object exhibiting a magnetization. Therefore, the utility of the NMR spectroscopic imaging is expected in that a plurality of distinct spin distribution images for nuclides of interest can be obtained depending on the difference in the chemical coupling states of the nuclides. One of methods of performing such an NMR spectroscopic imaging at a high speed equivalent to a usual MR imaging is disclosed in Journal of American Chemical Society, 107, 2817 (1985) by some of the present inventors. In the disclosed method, it is necessary to continuously inverting a field gradient during the signal measurement. However, the realization of an ideal inversion of the field gradient is practically impossible, especially in a large size of NMR imaging apparatus. Accordingly, in the large size of NMR imaging apparatus, it is necessary to employ a trapezoidal field gradient inversion sequence instead of the rectangular field gradient inversion sequence. A cosine-like field gradient inversion sequence may also be employed. In this case, however, it is necessary to separately measure the waveform of the field gradient and to perform a special signal processing based on the measured waveform data (See Journal of Magnetic Resonance, 42, 193 (1981)).